A low rate of penetration of drug through the skin is one of the major obstacles to the development of transdermal delivery systems. In many cases, the area of the skin which must be in contact with drug is prohibitively large unless the rate of penetration is increased.
Various compounds or compositions have been found to increase the rate of penetration of particular drugs. For example, U.S. Pat. No. 3,527,864 discloses that dimethylsulfoxide and homologous low molecular weight sulfoxides, when used in solvent concentrations, e.g. 50 percent or more, enhance the rate of penetration of various substances. However, these low molecular weight sulfoxides are absorbed systemically where they cause undesireable side effects. Said U.S. Pat. No. 3,527,864 claims the use of higher molecular weight (C.sub.8 -C.sub.13) sulfoxides in amounts of 0.1 to 10.0 percent by weight to enhance the penetration of various antimicrobial agents used for topical treatment.
U.S. Pat. No. 3,989,816 describes further agents useful for enhancing the rate of penetration of various topical medications or cosmetics. These agents are 1-substituted azacycloheptan-2-ones. Among these agents is 1-dodecyl-azacyclopentan-2-one, known as azone, which has found wide use in enhancing the rate of penetration through the skin of various medicaments. U.S. Pat. No. 3,787,571 describes the use of trichloroethanol and trifluoroethanol to enhance the rate of penetration of drugs and medications through the skin.
Applicants' invention provides means and compositions utilizing L-.alpha.-amino acids for enhancing the rate of penetration through the skin of both topical medicaments and of drugs employed for systemic administration.